Process of treating lignocellulosic material with organomercaptan



United States Patent Int. 'Cl. D21c 3/20 US. Cl. 162-76 20 ClaimsABSTRACT OF THE DISCLOSURE Methods of treating lignocellulosic materialfor the removal of lignin therefrom in a single phase, the stepsincluding (A) digesting said material with a treating liquor containingan organomercaptan such as thioglycolic acid in an amount correspondingto at least about 2 weight percent based on the weight of the oven-driedlignocellulosic material, the treating liquor also containing alkaliequivalent to at least about 2% effective alkali calculated as Na O, orat least 4 weight percent total alkali calculated as Na O, the ratio oftreating liquor to oven-dried lignocellulosic material and the time andtemperature of digesting such as to cause the organomercaptan to reactwith the lignin and concurrently to extract therefrom the resultingmercaptan-reacted lignin in a single stage to obtain a digested materialthat is amenable to refining to a pulp; and (B) removing the excessliquor from the treated material of step A.

This invention relates broadly to a process of treating lignocellulosicmaterial. More particularly it is concerned with a one-stage treatmentor digestion of lignocellulosic material with a treating or cookingliquor comprising an organic thio compound, especially anorganomercaptan, e.g., thioglycolic acid (TGA), HSCH COOH. A singleorganomercaptan or a plurality of different organomercaptans may beemployed; or, one or more organomercaptans may be used in conjunctionwith one or more inorganic treating agents including, for example,sodium sulfhydrate (sodium hydrosulfide, NaSH), sodium sulfide, sodiumpolysulfide, Na S sodium borohydride, NaBH and the like.

It was known prior to the present invention to digest or cook wood,specifically spruce sawdust, with an organomercaptan, more particularlyTGA. See, for example, Ingeniiirs Vetenskaps Akademien, Proceedings No.103, 75 pp. (1930), The Mercaptans of Pine Wood, by Bror Holmberg.Holmbergs procedure was to treat, for instance, spruce sawdust with asolution containing TGA and hydrochloric acid.

In our copending application Ser. No. 605,978, filed concurrentlyherewith and assigned to the same assignee as the present invention, wehave disclosed and claimed a two-stage treatment of lignocellulosicmaterial with a treating liquor containing an agent reactive with thelignocellulosic material and which is comprised of a specified minimumamount of an organomercaptan. In this method the treating liquor has aninitial pH not exceeding 12.0, and the time and temperature of thetreatment of the lignocellulosic material with this treating liquor issuflicient to convert the said lignocellulose material to a treatedmaterial containing mercaptan-reacted lignin. After removing the excessliquor from the treated material resulting from this first-stagetreatment, a second-stage treatment is applied whereby theorganomercaptan-reacted lignin retained by the digested lignocellulosicmaterial is extracted by contacting the residue with an extractiveamidogen compound, e.g., an alkanolamine, aniline, urea, and the like.

ice

The present invention differs from the known prior art and from ouraforementioned copending application it that a one-stage treatment isapplied to the lignocellulosir material, using a treating liquor of thekind broadly described in the first paragraph of the specification.

The invention is based on our discovery that a digestion or cooking ofWood (lignocellulosic material) with a treating liquor comprising anorganomercaptan, thereby to react the said mercaptan with the lignin inthe wood and obtain a solid product amenable to refining to a pulp withgood paper-making characteristics, can be effected in a single stage bycarrying out the digestion in a particular way that includes thehereafter-described highly alkaline conditions. The highly alkalineconditions of the treating liquor (initially and, usually, only ofslightly lesser alkalinity at the end of the digestion period) are suchthat there is present in the treating liquor at least 2 weight percenteffective alkali calculated as Na O, or at least 4 weight percent totalalkali also calculated as Na O. These minimum weight-percent values arebased on the weight of the oven-dried (O.D.) lignocellulosic material.

The terms effective alkali and total alkali as used herein have themeanings commonly employed in the pulping and paper-making art. As usedin this art, effective alkali for sulfate pulping means NaOH plusone-half of any Na s; while total alkali includes Na Co and one-half ofany Na SO in addition to all of the NaOH and Na S that may be present(reference: TAPPI-l203). In all cases, the amount of the said alkali(i.e., effective alkali or total alkali), the ratio of treating liquorto 0D. lignocellulosic material, and the time, temperature, and pressureof digestion are such as to cause the said organomercaptan to react withthe lignin in the said lignocellulosic material and concurrently toextract therefrom the resulting mercaptan-reacted lignin so that thereis obtained in a single-stage a digested, solid, cellulose-containingmaterial that is amenable to refining to a pulp, more particularly apaper-making pulp. (Parenthetically it may here be stated that the termactive alkali which is mentioned later herein differs from effectivealkali, as these terms are commonly used in the pulping and paper-makingart, in that it includes NaOH plus all Na s that may be present insteadof only one-half of any Na s; see the aforementioned referenceTAPPI-1203.)

The amount of effective alkali in the treating liquor may range, forinstance, from 2 to about 250 or more weight percent, calculated as NaO, and based on the weight of the OD. wood (lignocellulosic material) atl/w (liquor-to-wood) ratios of 1.5 :1 to 20:1; but ordinarily issubstantially above 6 weight percent (e.g., from 6.5, 7, or 8 to about65 or weight percent), calculated and on the same weight basis justmentioned, at l/w ratios of 2:1 to 9:1. The amount of total alkali inthe treating liquor may range, for example, from 4 to about 400 or moreweight percent at l/w' ratios of 1.5:1 to 20: 1; but ordinarily issubstantially above 7 weight percent (e.g., from 8 or 10 to about or ormore weight percent at l/w ratios of 2:1 to 9:1. These percentages, likethat .of the weight percent of effective-alkali, are calculated as Na Oand are based on the weight of the lignocellulosic material.

Surprisingly and unobviously, the technique of cooking a lignocellulosicmaterial with a highly alkaline treating liquor containing anorganomercaptan is more specific in delignification and provides higheryields of pulps of good papermaking characteristics then is obtainableby the Kraft process; the resulting pulps, especially under selectedconditions, can be made into brighter papers; and a lignin isrecoverable that is different in characteristics from Kraft-processlignin.

A primary advantage in using an organomercaptan as component of atreating liquor that contains alkali is mat the organomercaptan not onlyreacts with the lignin 1 the lignocellulosic material (making it moresoluble 1 the alkaline liquor) but also functions as a pH control yreason of buffering action of its --SH groups. For lese reasons, the useof such treating liquors for pulp- 1g wood and the like decreases theloss of carbonydrate laterial that normally results from degradation byalkali .uring delignification and thereby provides higher pulp ields.

In practicing the present invention, any wood or other ignocellulosicmaterial, or mixtures thereof in any proortions, may be cooked ordigested with an organomeraptan, with or without first removing theextractives by reating the lignocellulosic material in sub-divided forme.g., in the form of sawdust, and/or shavings, wafers, r chips) with anorganic solvent capable of extracting he water-soluble components of thematerial. Such lignolellulosic materials include softwoods, hardwoods,and ibrous annual plants. Examples of soft-woods are balsam ir, easternhemlock, jack pine, eastern white pine, red tine, black spruce, redspruce, white spruce, tamarack, tnd cypress. Example of hardwoods areblack gum, quakng aspen, mixing tomahawk, American beech, paper airch,yellow birch, eastern cottonwood, sugar maple, lilver maple, yellowpoplar, black cherry, and white oak. Examples of fibrous annual plantsare bagasse, =hemp, ll'ld jute. Mixtures of woods or otherlignocellulosic maerials of different origins may be used if desired,e.g., nixtures of different softwoods, or of different hardvoods, or ofone or more softwoods and one or more iardwoods.

Illustrative examples of organomercaptans that may )6 used to obtain adigested wood containing mercaptanreacted lignin are those embraced bythe general fornula wherein R represents a divalent radical, moreparticularly a divalent hydrocarbon radical, Y represents a monovalentsubstituent bonded directly to R, and n represents a numeral rangingfrom up to the combining power (i.e., a value that will completelysatisfy all valances) of the divalent radical represented by R.

Illustrative examples of divalent radicals represented by R in Formula Iare divalent hydrocarbon radicals and, more particularly, divalentaliphatic, e.g., ethylene, propylene (trimethylene), butylene,isobutylene, pentylene, isopentylene, decylene, etc., including divalentcycloaliphatic, e.g., cyclopentylene, cyclohexylene, cycloheptylene,etc.; divalent aromatic, e.g., phenylene, naphthylene, etc., divalentaliphatic-substituted aromatic, e.g., 2,4-tolylene, ethyl-2,5-phenylene,isopropyl-3,34-phenylene, l-butyl-2,4-naphthylene, etc.; divalentaromatic-substituted aliphatic, e.g., phenylethylene, phenylpropylene,naphthylisobutylene, xylylene, etc.; and radicals that may be classedeither as divalent aromatic-substituted aliphatic or divalentaliphatic-substituted aromatic, e.g., 4,a-tolylene, 3,;8-phenyleneethyl,4,u-xylylene, 2,gamma-phenylenebutyl, etc. Thus R may represent adivalent hydrocarbon radical represented by the general formula where Arrepresents an arylene radical and R represents an alkylene radical.Preferably the divalent hydrocarbon radical represented by R containsnot more than 10 carbon atoms, more particularly from 1 to 8 carbonatoms.

It is not essential that the divalent radical represented by R becomposed solely of carbon and hydrogen atoms. For example, the chain ofcarbon atoms, whether straight-chain aliphatic or carbocyclic, may beinterrupted in the chain by other atoms, e.g., by oxygen and/ or sulfurand/or nitrogen atoms bonded directly to carbon atoms of the chain.

Illustrative examples of substituents represented by Y in Formula I arefunctional groups such as --OH; CN; SH; COOH; COOR', Wherein R is amonovalent hydrocarbon radical corresponding to the divalent hydrocarbonradicals represented by R in Formula II;

.--COOM, wherein M is a salt-forming cation, e.g.,

NH or Na, K, Li, or other alkali metal, a salt-forming amine such asmono-, di-, or tri-(hydrocarbon-substituted) or-(hydroxy-hydrocarbon-substituted) amine, or other salt-forming cation,and especially those which yield water-soluble salts when present in theparticular thio compound. Or, Y may be a radical represented by (III)HSR wherein R represents a monovalent radical, more particularly amonovalent hydrocarbon radical corresponding to the divalent hydrocarbonradicals represented by R in Formula I. Illustrative examples ofmercapto compounds embraced by Formula III are the alkyl (includingcycloalkyl) aralkyl, aryl, and alkaryl mercaptans, more particularlythose which contain from 1 through 10 carbon atoms and especially thosehaving not more than about 8 carbon atoms.

The relatively low water-solubility of the unsubstituted hydrocarbylmercaptans embraced by Formula III make them much less suitable for usethan substituted hydrocarbyl mercaptans having one or more polar orsolvating substituent groups. However, if water-solubility of themercapto reactant is unimportant, e.g., when it is to be used inundiluted state, or in solution in an organic solvent (e.g., ethanol) orin a mixture of water and an organic solvent in which mixture theunsubstituted hydrocarbyl mercaptan is adequately soluble, then amercaptan within the scope of Formula III may be employed as a treatingagent.

Particularly useful in practicing the present invention areorganomerc-aptans represented by the general formula wherein Zrepresents an alkylene (including cycloalkylene) radical containing from1 through 10, and preferably from 1 through about 8, carbon atoms; Rrepresents a member of the group consisting of (a) hydrogen, (b) alkylradicals containing not more than about 10 carbon atoms and preferably alower alkyl radical (e.g., an alkyl radical containing from 1 throughabout 6 carbon atoms); and (c) a salt-forming cation, examples of whichhave been given hereinbefore with reference to M in the grouping --COOMwhich may be a substituent represented by Y in Formula I; and nrepresents an integer from 1 up to that of the combining power of thealkylene radical represented by Z. The alkylene radical represented by Zmay be straight-chain, branched-chain, or cyclic as in, for example,cyclopentyl, cyclohexyl, and the like.

More specific examples of mercapto compounds embraced by Formula IV aremonocarboxylic and polycarboxylic acids such as those having theformulas (VII) HS-CH-C O OH O OH (VIII) (CH3)2CCO OH OOH ( HS-CH-C 0 OHthe ammonium, alkali-metal (sodium, potassium, lithium, etc.) and otherwater-soluble salts of the aforementioned monoand di-carboxylic acids;and the cyclopentyl and cyclohexyl esters, as 'well as the methyl,ethyl, and propyl through pentyl (normal or isomeric alkyl) esters ofthe aforesaid acids. In the case of the salts and esters of thedicarboxylic acids, one may use either the monoor di-salt, or a mixturethereof, or a monoor diester, or a mixture thereof.

As the organomercaptan reactant we prefer to use thio acids, or salts oresters thereof represented by the general formula (XI) HS(CH -COORwherein n represents an integer from 1 to 6, inclusive, moreparticularly from 1 to 4, inclusive, and R has the same meaning as givenabove with reference to Formula IV. Thus, compounds embraced by FormulaXI may be the thio acid itself or a salt (especially a water-solublesalt) or an ester of such an acid. Of these compounds thioglycolic acidand the water-soluble salts and the lower alkyl esters thereof are themore preferred sub-group. Mixtures of acids and/or salts and/or estersembraced by Formula XI may be used if desired.

Instead of using organomercaptan compounds that are within the scope ofFormula XI, one may employ those wherein the COOR group in that formulahas been replaced by other hydrolyzable or solvating groups such as OH,-CN, SH,

R Ill and to one of the divalent hydrocarbon radicals represented by Rin Formula I.

TREATMENT OF LIGNOCELLULOSIC MATERIAL WITH AN ORGANOMERCAPTAN Thetreatment of wood or other lignocellulosic material with anorganomercaptan is described in, for example, the aforementionedHolmberg publication. Other methods of treating wood and otherlignocellulosic materials with an organomercaptan are described in, forin stance, the copending application of Carl A. Johnson, Ser. No.606,024, filed concurrently herewith and assigned to the same assigneeas the present invention.

In practicing the instant invention, the digestion with the treatingliquor (white liquor) may be elfected, as previously has been mentioned,with or without first removing the extractives including tall oil.Advantageously, the extractives are first removed by pre-extracting thewood or other lignocellulosic material with an organic solvent,preferably isopropanol, n-butanol, or other highboiling organic solvent.If a hot fluid medium, e.g., steam, is used to remove the aforesaidorganic solvent, it is desirable that the wood in subdivided (e.g.,chip) form remain in swollen state before digestion in the cookingliquor in order to facilitate diffusion of the liquor into the chips andthorough impregnation of the latter.

Chemical treatment with the organomercapto compound may be eifected at atemperature within the range of, for instance, from about to about 250C., more particularly from about to about 210 C., and preferably at atemperature of l50190 C. (The foregoing temperatures refer to the peakor maximum temperature after the cook has been raised to saidtemperature.) The time of digesting or cooking the lignocellulosicmaterial at the maximum temperature varies, for example, from a fewminutes (e.g., 3-5 minutes) to 6 hours or more.

The time period and the reaction temperature depend upon suchinfluencing factors, as for instance, the type, amount, andconcentration of the organomercapto compound in the treating liquor, thetype and degree of division of the lignocellulosic material beingtreated, the type and size of digester used, the degree of reactiondesired, and other influencing factors. In all cases the cooking timesand temperatures are correlated so that the wood or otherlignocellulosic material is digested and the lignin concurrentlyextracted to an extent such that it is unnecessary to apply asecond-stage or extract (lignin-extraction) treatment to thesingle-stage extracted wood or the like. Generally the desired degree ofdigestion is effected by cooking the lignocellulosic material in thetreating liquor for from about A to about 3 hours at a maximumtemperature of from about or C. to about 190 C., e.g., for from about /2hour to about 1 or 1 /2 hours at a temperature of approximately C.i10 C.

The digestion of the lignocellulosic material may be effected underatmospheric, subatmospheric or superatmospheric pressure, or under anycombination of these pressure conditions as desired, or as conditionsmay require. For example, if desired, vacuum may be applied initially tothe system in order to facilitate diffusion of the treating liquor intothe lignocellulosic material in chip or other subdivided form. In lieuof or in addition to such initial vacuum impregnation or treatment, thesubdivided lignocellulosic material may be soaked at atomsphericpressure and at ambient or an elevated temperature for a short or a longtime interval, followed by digestion in an autoclave under autogenous,superatmospheric pressure. Digestion in an autoclave at a temperaturewithin the aforementioned temperature ranges is a satisfactorytechnique. The existing pressure at a particular temperature is thenprimarily dependent upon the vapor pressures of the volatile componentsof the treating liquor at that temperature.

The proportion of organic thio treating agent, e.g., TGA, with respectto oven-dried (O.D.) lignocellulosic material may be within the rangeof, for example, from about 1:1 (i.e., about 50% by weight of each toabout 2:100 to 2.5: 100 (i.e., 2.5% by weight of the organomercaptanreactant based on the weight of the OD. lignocellulosic material). Theupper limit of the organomercaptan component is not critical, butbecause of its relatively high cost it is economically desirable to usenor more of it in the cooking liquor than is required to effect thedesired result. Hence there are economic advantages in restricting theupper limit of the amount of organomercaptan to not more than about 50%,more particularly to not more than about 30 or 35%, by weight of the OD.lignocellulosic material. Advantageously, TGA or equivalent (in itseffectiveness as a reactant) organomercaptan is employed in an amountcorresponding to from about 5 to about 20 or 25 weight percent based onthe weight of the OD. lignocellulosic material.

The amount of TGA or equivalent organomercaptan employed is preferablyabout the same as or near to the equivalent amount of the effectivealkali in order to obtain the maximum benefit of carbohydrate protectionduring the digestion period. (For example, when the treating liquorcontains 16% effective alkali and the liquor-towood ratio is 4.5/1,i.e., a ratio of treating liquor to D. gnocellulosic materialcorresponding to 45 ml. of the ormer for each grams of the latter, thenthe liquor ontains an excess of 0.516 mole NaOI-l per 100 g. wood; .ndthe equivalent amount of TGA would be 47.5 g. per 00 g. Wood.) Whenlarger amounts of TGA or equivlent organomercaptan are employed, lesssevere cooking onditions are, in general, required; and the maximumlenefit of pH control and protection of the carbohydrate omponent of thelignocellulosic material is secured.

The substantially pure organic thio compound, or a rude form thereofsuch as is obtained commerically in ts preparation, or mixtures oforganic thio compounds nay be employed as the reactive agent orcomponent of he treating liquor. Minor amounts (less than 50% by veight)of inorganic thio reactants, e.g., sodium sulfhylrate, sodium sulfide,sodium polysulfide, etc., may be lsed in the form of an admixture withthe organic thio compound.

Water is preferably used as the liquid reaction melium of the mercaptancooking liquor. However, other nert solvents or mixtures of insertsolvents may be em- )loyed if desired. 9

The effective alkali concentration of the treating liquor s preferablyadjusted by the addition of sodium or other tlkali-metal hydroxide, orwith other alkaline substances {singly or a plurality thereof), e.g.,hydroxides of alkainc-earth metals within which term are herein includedlot only calcium, strontium and barium but also maglesium.

The ratio of the treating liquor to the OD. lignocel- .ul0sic materialmay be considerably varied but usually :he ratio corresponds to fromabout 25 or 30 to about 90 or 100 m1. of the former for each 10 grams ofthe latter, more particularly from about 30 to about 60 ml. of theformer for each 10 grams of the latter. Good results iave been obtainedusing a so-called liquor-to-wood ratio of 4.5 to 1; that is, a ratiocorresponding to 45 ml. of treating liquor for each 10 grams of wood(lignocellulosic material).

The type of reaction vessel required for the cook depends upon suchinfluencing factors as, for example, the conditions of the cook, theproperties of the organomercaptan reactant, and the vapor pressure andalkalinity of the cooking liquor.

In carrying out the treatment of the lignocellulosic material with theorganomercapto compound, the lignocellulosic material, in a suitablysubdivided form, is saturated and/or covered with, or suspended in, aliquor containing the organomercapto compound alone or admixed withinorganic thio reactants or other chemicals, examples of whichpreviously have been given. It is then cooked or digested for a periodof time and at a temperature and pressure which depend upon suchinfluencing factors as have been mentioned hereinbefore.

At the end of the cooking period, the alkaline spent liquor (blackliquor), and which contains the mercapto reacted lignin andhemicellulose, is preferably recoverd, e.g., by draining from thetreated wood or the like in chip or other sub-divided form. The chipsare thoroughly washed, e.g., with hot water, to remove any spent liquorcontaining mercaptan-reacted lignin and unreacted mercapto (includingorganomercapto) compound.

The lignin may be recovered from the spent liquor by precipitation withcarbon dioxide or a mineral acid, e.g., hydrochloric, sulfuric, nitric,etc. The lignin that precipitates is filtered off. The filtrate containsunreacted mercapto compound. This filtrate may then be concentrated, forexample by removal of the solvent (H O); or by the addition of make-upchemicals including, for example, eflfective alkali, organomercaptocompound and, also, of inorganic thio reactant material if the latterwas a com ponent of the fresh treating liquor. This concentrated liquormay be recycled in the process.

Dialysis also may be employed to separate the lignin from the spentliquor. Or, the liquor containing the dissolved lignin may be passedthrough an anion-exchange resin in free-base form thereby selectively toadsorb on the resin anionic materials contained in the liquor while thelignin in purified form passes through the resin for subsequentevaporation of the eluate and recovery of lignin. This latter techniqueis more fully described and broadly and specifically claimed in thecopending application of William H. Greive and Karel F. Sporek, Ser. No.418,872, filed Dec. 16, 1964, now abandoned and assigned to the sameassignee as the present invention. The lignin-free liquor resulting fromtreatment of the lignincontaining spent liquor with anion-exchange resinmay then be recycled in the process after adding any necessary make-upchemicals.

Instead of allowing the unreacted organomercaptan compound to remain inthe lignin-free spent liquor and reusing it directly, after addingmake-up organomercaptan (plus other chemicals if necessary), theunreacted organomercapto compound may be recovered from the lignin-freeliquor by distillation or by further concentrating it if necessary, andthen extracting the residue with a solvent for the unreactedorganomercaptan, e.g., alcohol, ether or other organic solvent in whichthe particular organomercaptan is known to be soluble.

A typical overall process for the treatment of lignocellulosic material,e.g., wood in chip form, in accordance with this invention is outlinedbelow:

(1) Pre-extract the wood for the removal of organicsolvent solubleextractives such as tall oil and the like. (Optional) (2) Immerse thechips (in swollen state if step 1 has been used) in the aqueousorganomercaptan-containing treating liquor adjusted to, by weight, above2% (more particularly above 4%) effective alkali or above 4% (moreparticularly 6.5% and above) total alkali, calculated as Na O, and basedon the OD. weight of the lignocellulosic material.

(3) Digest the chips for from a few minutes to 6 hours (preferably fromA1 to 3 hours) at l00250 C. (preferably at l50190 C.) maximumtemperature to obtain pulp.

(4) Remove the organomercaptan-reacted lignin from the spent digestionliquor.

(5) Reuse the remaining lignin-free liquor, after adding such make-upchemicals as may be necessary, for treating additional wood or otherlignocellulosic material.

The above-mentioned overall process may be carried out continuously,semi-continuously or by batch technique. The process is especiallyadapted for use in a continuous, rapid, vapor-phase digestion or pulpingoperation. Such a vapor-phase procedure has the advantages of bothminimizing the time of cooking and the amount of chemicals required inthe treating liquor, thereby providing distinct economic advantages.Thus, the pre-ex- 'tracted chips (swollen with water, isopropanol and/orother organic solvent used in the pre-extraction), and while still hot,may be so impregnated with the highly alkalineorganomercaptan-containing treating or white liquor that the amount ofliquor absorbed by the chips is sufi'icient for pulping. The excessliquor is then drained from the chips, and the chips are rapidly broughtto the maximum temperature of digestion (e.g., -190 C.) by contact withhigh-pressure steam.

The washed, digested, subdivided lignocellulosic material, or crudepulp, regardless of whether it has been produced by a continuous orsemi-continuous method or by a batch technique, is mechanicallydefibrated in the presence of water if it has not already beeneffectively defibrated to a suitable pulp. The resulting pulp is thenusually screened to remove the residual liquor and to provide a moreuniform pulp. Further washing of the pulp may be effected if deemednecessary in view of the particular contemplated end use. Bleachingand/or drying steps are likewise optional depending upon the end use.

If bleaching is to be effected, it is usually done before drying thepulp. Prior to a bleaching step the pulp may be washed with a diluteaqeuous solution of an inorganic acid, e.g., a aqueous HCl solution,thereby to provide a more complete and efficient bleaching action thanwhen bleaching is effected in the absence of such a dilute acid wash.The pulp, with or without further treatment as may be required for theparticular end use, is then suitable for utilization in making anydesired cellulosic product including, for example, paper and relatedproducts, cellulose acetate, cellulose xanthate, regenerated cellulose,etc.

In order that those skilled in the art may better understand how thepresent invention can be carried into effect, the following examples aregiven by way of illustration and not by way of limitation. All parts andpercentages are by weight unless otherwise stated.

EXAMPLE 1 This example illustrates the pulping of a softwood,specifically isopropanol-extracted Southern pinewood, using a treatingliquor comprised of (a) a relatively low concentration of anorganomercaptan, specifically TGA, which was converted to sodiumthioglycolate (NaTGA) in the treating liquor, and (b) a high content ofeffective (and active) alkali. A soda cook at the same effective andactive alkali concentration is made under the same cooking conditionsfor purpose of comparison.

The apparatus and general procedure for making these cooks are asfollows:

For each cook a 400.0 g. charge (based on the OD. Weight) of air-driedSouthern pine chips from which the isopropanol-soluble extractivespreviously have been removed, and a total of 1800 ml. of aqueous liquorcontaining the chemicals set forth in Table IA in an amount based on theweight of the charge of 0D. wood chips, are charged into a stationarydigester. The mixture, which is at a liquor-to-wood ratio of 4.5 to 1,is heated to 170 C. With a steady rise of temperature from 100 C. to 170C. over a period of 43-47 minutes. It is maintained at 170 C. under thepressure generated by the mixture for 39 minutes. The mixture is thencooled to approximately 100 C. over a period of about 1 hour, afterwhich the charge is removed from the digester and drained through ascreen to separate the solid residue from the spent liquor. This residueis soaked and washed with hot water, defibrated and then given a finalwashing.

The wet cellulosic pulp obtained as described above is dried to 2030%solids, then made into 8" x 8", 26 lb./ MSF basis weight hand sheets fortesting in the following manner: At least three aliquots of theexperimental pulp, in an amount based on the OD. weight of the wet pulp,are refined with water at 1% consistency for varying periods of time ina Mead Laboratory Refiner (manufactured by the Bauer Bros. Company,Springfield, Ohio). The degree to which each pulp aliquot is refined, asdetermined by measuring the drainage rate of the pulp in a SlownessTester" (manufactured by Williams Apparatus Company, Watertown, N.Y.),is controlled as much as possible so as to provide three or morerefining points uniformly mixed prior to making the handsheets. Thesheets are formed in an 8" x 8" Williams sheets mold from aliquots ofthe pulp slurry that are measured volumetrically for producing 26lb./MSF sheets. The pulp consistency on forming the sheets is adjustedto 0.05% by further dilution of the pulp aliquot in the mold. The sevenor more sheets (wet webs) formed from each batch of pulp slurry arecouched from the wire of the mold onto standard 12" x 12" TAPPIblotters, then stacked between blotters with six blotters separating thesheets. The stack is then pressed for 5 minutes at 150 p.s.i.g. pressureon a Williams press (manufactured by Williams Apparatus Company). Thepressed sheets, retained on the couch blotters, are dried at 260-280 F.on a steamheated Noble and Wood drier, with the sheet contacting thedrum for approximately 2 minutes. After removing the blotters, the driedsheets are conditioned at 50% relative humidity and F. for a minimum of24 hours before testing.

More detailed information on the operating conditions and the results isgiven in Table IA. In all three cooks the liquor-to-wood ratio Was 4.5to l, and the cooking time was 39 minutes at the maximum temperature of170 C. The value for the pulp characteristic listed as Lignin is theresult obtained when the pulp is tested for acid-insoluble lignin usingthe apparatus and procedure set forth in TAPPI Standard Test Method T222m-54. The Williams Slowness test, which measures the rate in seconds perliter at which one liter of pulp at 0.3% consistency drains at 20 C. inthe Williams Slowness instrument, is used in the manner previouslydescribed in order to measure the degree to which the pulp was refinedin the Mead refiner. The time in seconds for refining the pulp in theMead refiner to 55 seconds Williams Slowness, as determined from thethree or four refinings made, is listed in the column of Table IA headedMead Refine Time.

The results of tests on papers (handsheets) made from the pulps producedas described in Table IA are given in Table IB. The values for the papercharacteristics listed under the columns headed Tensile, Mullen, Tear,Ring Crush and Brightness are the results obtained when the respectivehandsheets are tested using apparatus and procedures set forth whereindicated below:

Density, T APPI Standard: T411 m44 Basis Weight, TAPPI Standard: T410os61 Tensile, TAPPI Standard: T404 os61 Tear, TAPPI Standard: T414 ts-64Mullen, TAPPI Standard: T403 ts-63 Ring Crush, TAPPI Standard: T472 m-51Brightness, TAPPI Standard: T452 m-58 The only exceptions from theabove-identified test methods are that only 5 sheets, each 49 squareinches in area, are used in the Density and Basis Weight tests.

The tabulated values are adjusted for 26 lb./MSF basis weight paper andfor pulp refined to 55 seconds Williams Slowness. The values in TablesI, II, III, IV and VI are determined from the results of tests on foursets of handsheets made from each test pulp as described above. Thevalues in Table V are from 3 sets of handbracketing 55 seconds WilliamsSlowness. Each of the sheets. refined pulp slurries is diluted to 0.5%consistency and Tables IA and IB follow.

TABLE IA.

Soda and TGA Cooks of Southern Pinewood at 16% Effective Alkali 1Cooking Conditions Pulp Data Pulp Carbohydrate Pnlp (Percent of YieldLignin Initial Cook No. Chem./ g. Wood pH Range (Percent) (Percent) O.D.wood) 1a 20.7 g. NaOH, 5.0 g. NazCOa 13.5 to 13.3.- 62. 7 24. 4 47. 49.8 g. NaTGA, (7.9 g. TGA), 20.7 g. NaOH, 5.0 g. NazCO3 13.5 to 13.2..60. 3 19. 9 48. 3 9.8 g. Na/IGA, (7.9 g. TGA), 20.7 g. NaOH, 0.5 g.NazCO 13.5 to l3.0 60. 3 19. 5 48. 5

1 Calculated as NazO and based on the OD. weight of the wood.

1 NaT GA=Sodium Thioglycolate.

TABLE I-B Tests on 26 IbJMSF Papers Made from Pulps of Cooks of TableI-A Papers Mead Williams Dry Ring Bright From Refine Slowness DensityTensile Tear Mullen Crush ness 300k No. Time (Sea) (See) (p.c.f.)(lbs/in.) (g./16 sh.) (p.s.i.) (lbs) (percent) l-a 193 55. 27. 8 39. 14771 51. 5 19. 7 H3 171 55. 0 30. 3 46. 2 177 88 68. 0 19. 2 H: 186 55. 030. 6 45. 4 184 87 67. 0 18. 8

The results given in Tables I-A and I-B demonstrate the effect that arelatively low charge of TGA (converted to NaTGA in the cooking liquoras in all other examples herein wherein the charge included TGA) has inthe pulping of a softwood, specifically Southern pine, in a single stagewith the liquor at a high (specifically 16% as Na O based on the OD.wood) effective alkali content. The lower lignin and higher residualcarbohydrate content of the pulps obtained from the TGA cooks (i.e.,Cooks 1-b and 1c) compared to that of the pulp from the caustic sodacook, viz., Cook 1a, which was carried out under comparable cookingconditions and with the same concentration of eifective alkali, show theimproved selectively and faster rate of delignification that areprovided when an organomercaptan reactant is included in the alkalinetreating liquor.

From the data given in Table I-B it will be noted that the papers madefrom the pulps of Cooks 1-b and 1-c wherein TGA in the form of a sodiumsalt thereof was a component of the treating liquor, showed greatlyincreased strength characteristics as compared with the paper made fromthe pulp of soda Cook 1-a. Furthermore, the former papers approachedthat of high-strength kraft paper in Mullen, tensile, tear and ringcrush values.

EXAMPLE 2 This example illustrates the preparation of pulps in one-stagefrom Southern pinewood with the alkaline liquor comprised of higherconcentrations of organomercaptan, specifically TGA as sodiumthioglycolate, than was used in Example 1. The effective alkaliconcentration of the liquor, the temperature of digestion, the apparatusused and the general procedure are the same as described in Example 1.The time of digestion is varied from 39 to 58 minutes. As in Example 1,the temperature of di gestion is 170 C. and the liquor-to-wood ratio is4.5 to 1.

More detailed information on the cooking conditions and on the resultsobtained are given in Tables I'IA and III-A. The results of tests onhandsheets made from pulps produced as described in Tables II-A andLII-A are given in Tables II-B and III-B.

Tables II-A, IIB, III-A and III-B follow.

TAB LE II-A TGA Cooks of Southern Pinewood at 16% Effective AlkaliVariation of TGA Charge Cooking Conditions Pulp Data Pulp CarbohydratePulp (percent of Cook Time Yield Lignin Initial 0.D. No. Chem./ g. WoodpH Range (min.) (percent) (percent) Wood) 2-a 18.6 g. NaTGA, (15.0 3963. 20. 8 49. 9 2- 24.8 g. NaTGA, (20.0 39 63. 7 21.0 50. 3 2-e. 43.4 g.NaTGA, (35.0 39 64.9 19.9 52.0 2-d- 61.9 g. NaTGA, (50.0 39 62. 4 16. 252.3 2-e 123.9 g. NaTGA, (100. g. 39 57. 9 10.7 51.7

1 See Footnote to Table I-A.

TABLE II-B Tests on 26 lb./MSF Papers Made from Pulps of Cooks of TableII-A Mead Papers Refine Williams Dry Ring Bright- From Time SlownessDensity Tensile Tear Mullen Crush ness Cook No. (See) (See) (p.e.f.)(lbs/in.) (g./l6 sh.) (p.s.i.) (lbs.) (percent) TABLE III-A T GA Cooksof Southern Pinewood at 16% Effective Alkali Variation of T GA ChargeCooking Conditions Pulp Data Plup Carbohydrate Pulp (Percent of Cook pHTime Yield Lignin Initial O.D. No. 0hem./100 g. Wood Range (min)(percent) (percent) Wood) 3-a 123.9 g. NaT GA, (100.0 g. TGA), 20.7 g.NaOH 9.8 9.7 39 57. 9 10. 7 51.7 3-b 123.9 g. NaT GA, (100.0 g. TGA),20.7 g. NaOH 9.8 to 9.6-..- 58 57. 7 8. 8 52. 6

1 See Footnote to Table I-A.

TABLE III-B Tests on 26 lb./MSF Papers Made from Pulps of Cooks of TableIII-A Mead Refine Williams Dry Ring Papers From Time Slowness DensityTensile Tear Mullen Crush Brightness Cook No. (See) (See) (p.c.f.)(lbs/in.) (g./16 sh.) (p.s.i.) (lbs.) (percent) The data in Tables IIA,II-B, HIA, and III-B demonstrate the pulping, and show the improvementsthat result in one-stage alkaline pulping, of isopropanol-extractedSouthern pinewood with an alkaline treating liquor containing onorganomercaptan at a increased level above that employed in Example I.The effective alkali content of the liquors is maintained the same inboth Examples I and 2 at 16 weight percent calculated as Na O and basedon the weight of the OD. lignocellulosic material.

The pH data in Tables II-A and I'II-A show the effect that the mercaptogroups of TGA (sodium thioglycolate in the liquor) have in reducing andcontrolling the hydroxyl ion concentration of the alkaline pulpingliquor. The differences in the pH levels of the initial cooking liquorsprovide evidence that, as the TGA charge is increased (with comparableincreases in the amount of sodium thioglycolate in the individualcooks), more of the hydroxyl ions originating from the effective alkali(NaOH) are tied-up by the equilibrium reaction that may be illustratedas follows:

As pulping proceeds the hydroxyl ions that are consumed are replenishedby the resultant shift of the equilibrium in the above-describedreaction. The hydroxyl ion control (i.e., pH control), which is therebyprovided during the cook, is shown most pronouncedly by the low leveland small change of the liquor pH in Cook Nos. 2-d and 2-e in TableII-A, and in Cook Nos. 3-a (2-a' repeated) and 3-b of Table III-A inwhich the molecular amounts of the TGA charge (present in the liquor assodium thioglycolate) exceed that of the effective alkali (NaOH).

The pulping advantages provided by TGA (sodium thioglycolate in theliquor), as a result of its influence in controlling the hydroxyl ionconcentration of the cooking liquor and due to its reactivity with thewood lignin,

are shown by the pulp and paper data given in these tables.

The data on the pulps of the cooks reported in Tables IIA and II-B,which cooks were carried out under the same conditions of cooking time,temperature, and level of effective alkali, show that as the amount oforganomercaptan is increased (as in Cook Nos. 2-b through 2-e),delignification is more complete, i.e., there is less lignin left in thepulp; at the same time the carbohydrate yield (i.e., the amount ofresidual carbohydrate in the pulp) is advantageously increased. Thisgain in the carbohydrate yield provides evidence that theorganomercaptan, as a result of its control of the hydroxyl ionconcentration of the cooking liquor, is effective in decreasing thealkaline degradation and resultant loss of carbohydrate material thatordinarily occurs in highly alkaline pulping processes.

The results presented in Table III-A provide additional evidence of theaforementioned effect. Cook Nos. 3-a and 3-b shown in this table differfrom each other only in the time (39 minutes vs. 58 minutes) ofdigestion at the maximum digestion temperature of 170 C. The data showthat delignification continues as the cooking time is extended.Surprisingly and unobviously, however, there is no further loss ofcarbohydrate material and the high yield of pulp is substantiallymaintained (57.9% pulp yield for the 39-minute cook vs. 57.7% yield forthe 58- minute cook).

The pronounced improvements attained by the presence in the treatingliquor of thioglycoloc acid in the form of its alkali-metal,specifically sodium, salt will be readily apparent from a comparison ofthe pulp and paper data for the organomercaptan cooks shown in TablesIIA and -IIB with the corresponding soda Cook No. 1a presented in TablesI-A and IB. All these cooks were carried out under the same conditionsof time, temperature, and level of effective alkali.

It will be noted that the residual carbohydrate content of the pul-pswas increased from 47.4 weight percent of the initial O.D. wood in thecase of the soda Cook No. l-a to as high as 52.3 weight percent (CookNo. 2-d) of the initial O.D. wood as a result of including anorganomercaptan in the cooking liquor. It will further be noted that thelignin content of the pulps was decreased from 24.4% for soda Cook No.l-a to 10.7% in the case of Cook No. 2e that contained anorganomercaptan in the cooking liquor. As has been indicatedhereinbefore, this is because of the accelerated rate of delignificationthat occurs when an organomercaptan, specifically thioglycolate in theform of its sodium salt, is a component of the treating liquor.

In addition to, and as a result of, the aforementioned improvementsfroma delignification standpoint of the method of this invention, acomparison of the test data given in Tables II-A and II-B with that forthe soda cook given in Tables I-A and I-B shows that other beneficialand unobvious results are attained by including an organomercaptan inthe treating liquor.

Thus, it will be noted that at pulp yields both comparable to and higherthan the yield (62.7%) obtained in soda Cook No. 1a, e.g., at the62.464.9% pulp yields from organomercaptan Cook Nos. 2-a, 2-b, Z-c, and2-d, the pulps from the last-mentioned cooks contain much less lignin,specifically as low as 16.2% in the case of Cook No. Z-d as comparedwith the 24.4% lignin content of the soda pulp from Cook No. 1 a.Furthermore, the papers made from the pulps wherein the treating liquorcontained an organomercaptan had far superior strength characteristicsas compared with the paper made from the soda pulp, more particularly(at the same comparable and higher yields) 44.0-52.6 vs. 39.5 tensile;172-178 vs. 147 tear; -98 vs. 71 Mullen, and 54.7-69 vs. 51.5 ringcrush.

The data in Tables II-A, II-B, III-A, and IIIB also show that pulpsproduced by the method of this invention can be obtained in higheryields than by the Kraft process and yet can be made into papers havingstrength characteristics which, except for tear values, are comparableto those of papers made from Kraft pulp. Evidence of this fact is foundin the aforementioned tables, especially the data given with regard tothe pulps (and papers made therefrom) of Cooks 2-d, 2-e, 3-a (2-e), and3b; and a comparison of that data with corresponding data for laboratoryKraft cooks, more particularly Cook Nos. 6a, 6-b-, and 6-c as given inTables VI and VIB that are presented later herein and which cooks weremade at the same active alkali concentration as the cooks of Tables I,II and III. A comparative examination of the data shows that the methodof this invention provides pulps at yields of 57.7% to 62.4% (Cook Nos.2-d, 3a, and 3b) from which can be made papers having Mullen, tensile,and ring crush properties comparable to that of paper made from Kraftpulp in a yield of 55.9% Cook No. (6a). Also, papers made from theorganomercaptan pulps (referring particularly to the papers made fromthe pulps of Cook Nos. 2-c, 2-d, 3a, and 3b) are better in Mullen,tensile, and ring crush properties (i.e., have higher strength values)than those papers made from the Kraft pulps (Table VI-A and VI-B) atcomparable pulp yields.

Evidence that the process of this invention is more selective indelignification than is kraft pulping is also provided by the resultsfrom the above-identified cooks. This is shown by the fact that thepulps from the organomercaptan cooks (i.e., cooks wherein anorganomercaptan, specifically TGA in the form of a sodium salt thereof,was a component of the treating liquor) contain less residual lignin andmore carbohydrate material, at a given pulp yield, than do the Kraftpulps.

In addition, more rapid delignification than by kraft pulping under thesame cooking conditions of time, tem- Jerature, and level of activealkali is obtainable by the method of the present invention. Evidence ofthis fact is :ound in the low (10.7%) lignin content of theorgalomercaptan pulp from Cook No. 2e as compared with the substantiallyhigher value of 13.4% lignin content of the kraft pulp from Cook No. 6a.

EXAMPLE 3 This example illustrates the pulping of isopropanolextractedpinewood with treating liquors comprised of various concentrations of anorganomercaptan as in Example 2 but at a lower concentration ofeffective alkali, more particularly 8 weight percent, calculated as NaO, and based on the weight of the OD. pinewood, instead of 16 weightpercent effective alkali (on this same basis) as was employed inExamples 1 and 2.

The apparatus and general procedure are the same as described inExample 1. The digestion time is varied from 39 to 80 minutes at thesame maximum temperature of digestion, viz, 170 C., and the sameliquor-to-wood ratio of 4.5 to 1 as that employed in Examples 1 and 2.

More detailed information on the cooking conditions is given in TableIV-A. The properties of the handsheets made from the pulps described inTable IV-A are given in Table IV-B.

Tables IV-A and IV-B follow.

TABLE IV 16 desirable. It shows that less degradation of the cellulosehas occurred during digestion.

The results also show that a high yield of pulp having a good quality isproduced by the technique of this example. More particularly, the pulpand paper data show that from pulps obtained in yields of 65.466.6%there can be produced paper (handsheets) having better paper properties(except for tear strength) than can be made from kraft pulp at muchlower yields; and with properties that approach those of papers madefrom high-strength kraft pulp.

Thus, by comparing the pulp yield of 66.6% (and data on paper madetherefrom) of Cook No. 4-b in Tables IV-A and IV-B with correspondingdata for kraft pulp yields of 60.8 and 64.3%, respectively (and data onpaper made therefrom), of Cook Nos. 6b and 6c in Tables VI-A and VI-B,it will be noted that the paper made from the 66.6% yield oforganomercaptan pulp is higher in tensile strength (52.8 vs. 42.5-44.3),Mullen (95 vs. 81-90), and ring crush (approx. 66 vs. 60-65).

'Of particular significance is the fact that the addition of asufficient amount of an organomercaptan to the treating liquor gives anunbleached pulp from which can be made a paper that is much brighterthan can be made from a kraft pulp. This is shown by comparing the high24.6% brightness of the paper prepared from the pulp of Cook No. 4-b ofTable IV-B with that of the lower TGA Cooks of Southern Pinewood at 8%Etiective Alkali Variation of TGA Charge Cooking Conditions Pulp DataPulp Carbo- Pulp hydrate (Per- Coolr pH Tune Yield Lignin cent ofInitial No. Chem./100 g. Wood Range (min) (percent) (percent) O.D. Wood)4-a 31.0 g. Na'IGA, (25.0 g. TGA), 10.3 g. NaOH 9.5 to 9.4--.. 80 65. 420.1 52.3 4-1) 61.9 g. Nal GA, (50.0 g. TGA), 10.3 g. NaOH 9.5 to9.2--.- 39 66.6 18. 4 54. 3

1 See Footnote to Table I-A.

TABLE IV-B Tests on 26 lb./MSF Papers Made from Pulps of Cooks of TableIV-A Mead Refine Williams Dry Ring Papers From Time slowness DensityTensile Tear Mullen Crush Brightness Cook No. (See) (Sec) (p.c.f.)(lbs./1n.) (g./16 sh.) (p.s.i.) (lbs) (percent) 4-3, 162 55. 0 32. 3 48.0 166 91 64. 8 16. 8 4-b 152 55. 0 33. 7 52. 8 150 95 65. 8 24, 6

The results given in Tables IV-A and IVB again show the effectivenessthat an organomercaptan, specifically thioglycolic acid in the form of asodium salt thereof, has (under the conditions used in practicing thisinvention) with respect to delignification, protection of thecarbohydrate material during digestion and the obtainment of a highyield of pulp having good paper-making properties; and that such resultsare obtainable in the pulping of a softwood, specifically southernpinewood. using a treating liquor comprised of 8% effective alkali,calculated as Na O, and based on the weight of the OD. wood.

The low and narrow pH range of the treating liquors during cooks showthe control of the hydroxyl ion concentration (i.e., pH) provided by themercapto groups of the organornercaptan. Evidence of the benefit of thiscontrol, in addition to that shown in Examples 1 and 2, is found in thehigh (i.e., 52.354.3%) carbohydrate yields from these cooks, viz., CookNos. 4-a 4-b, as compared with soda Cook No. 1-a in Table I-A(carbohydrate yield of 47.4%) and with kraft Cook No. 6c in Table VI-A(carbohydrate yield of 51.1%). By comparison, the pulps from these kraftand soda cooks contain more lignin than do the organomercaptan pulps ofthis example (20.6% and 24.4% for the kraft and soda cooks,respectively, vs. ISA-20.1%). As indicated hereinbcfore, the higheryields of carbohydrate material are 17.818.8% brightness values of thekraft papers made from the pulps of Cook Nos. 6-a, 6-b, and 6c that aregiven in Table IV-B. The higher brightness value for paper made from theorganomercaptan pulp was obtained using a higher concentration oforganomercaptan in the treating liquor than was employed in carrying outCook No. 4-a shown in Tables IV-A and IV-B.

EXAMPLE 4 This example illustrates the pulping of isopropanolextractedsouthern pinewood with a treating liquor comprised of (a) a major amountof an organomercaptan, specifically TGA in the form of a sodium saltthereof, and (b) a minor amount of sodium sulfhydrate (NaSH). The activealkali content of the treating liquor is 11.3%. The effective alkalicontent of the cook containing both the organomercaptan and the sodiumsulfhydrate is 10.8%. A kraft-type cook with liquor comprised of ahigher concentration of NaSH (as Na S) and the same active alkaliconcentration is provided for comparison. In both kraft cooks and cooksof the present invention, the NaSH is present in the treating liquor asNaSH or Na s. This latter kraft treating liquor has an effective alkaliconcentration of 10.3%. The apparatus and general procedure are the sameas described in Example I. The time of digestion is minutes at themaximum temperature of 'C., and the liquor-to-wood ratio is 4.5 to 1.

More detailed information on the cooking conditions is given in TableV-A. The yields and properties of the pulps are also described in TableV-A while those of the handsheets made from the pulps are given in TableV-B.

Tables VA and V-B follow.

TABLE VA Kraft-Type and TGA plus NaSH Cooks of Southern Pinewood at11.3% Active Alkali 1 Cooking Conditions Pulp Data Pulp Carbo- EfiectivePulp hydrate (Per- Alkali pH Yield Lignin cent of Initial Cook No.Chem./100 g. Wood (Percent) Range (Percent) (Percent) O.D. Wood) 5-a18.6 g. NaT GA, (15.0 g. TGA), 0.9 g. NaSH, 13.9 g. NaH 10. 8 12.4 to11.0- 66.6 21.4 52. 3 5-b 2.5 g. NazS, (1.8 g. NaSH), 12.0 g. NaOH, 2.0g. N21200:; 10. 3 13.2 t0 12.7-- 66. 8 24. 4 50. 5

1 Calculated as N830 and based on the O.D. weight of the wood.

TABLE V-B Tests on 26 lbJMSF Papers Made from Pulps of Cooks of TableV-A Papers Mead Williams Dry Ring Bright- From Refine Slowness DensityTensile Tear Mullen Crush ness Cook No. Time (Sec) (Sec) (p.c.f.)(lbs/in.) (g./16 sh.) (p.s.i.) (lbs.) (Percent) The data in Tables V-Aand VB show the more selective and complete delignification that isobtained, and the improved properties of papers made from the resultingpulps, when the treating liquor employed in pulping a softwood,specifically Southern pinewood, is comprised of both (a) anorganomercaptan, more particularly TGA in the form of a salt thereof,and (b) a minor but substantial amount of NaSH as compared with theresults obtained using a synthetic kraft-type liquor under com parablecooking conditions of time, temperature, and active alkaliconcentration.

The improvement in delignification is shown by the fact that at thecomparable pulp yields (i.e. 66.6% and 66.8%) of these cooks, the pulpfrom organomercaptan/ NaSH Cook No. S-a contains less lignin (21.4% vs.24.4%) and more carbohydrate material (52.3% vs. 50.5% of the initialO.D. wood) than does the pulp from the kraft-type Cook N0. 5-b. The lowpH range of the treating liquor both initially and at the end of thecook and the high yield of carbohydrate in the pulp resulting fromorganomercaptan/NaSH Cook No. 5-a is evidence of the pH control anddecreased carbohydrate degradation obtained by practicing the method ofthis invention. 2

The data on the papers made from the respective pulps show (Table V-B)the better properties with respect to tensile strength (39.6 vs. 35.6),Mullen (81 vs. 77), and ring crush (69.0 vs. 54.1) that characterize thepapers prepared from the organomercaptan/NaSH pulp of Cook No. 5-a ascompared with those of papers made from the kraft-type pulp of Cook No.S-b.

EXAMPLE 5 of the pulps are given in Table VI-A. The results of tests onpapers (handsheets) made from the pulps identified in Table VI-A aregiven in Table VI-B.

FORMULATION FOR THE COOKS Chip Charge: 400.0 g. (O.D. weight) ofair-dried chips;

pre-extracted with isopropanol. Liquid Composition:

11.1. g.p.l. Na CO (2.9% as Na O on the O.D.

wood) 14.8 g.p.l. Na s (5.3% as Na O on the O. D.

wood) 30.7 g.p.l. NaOH (10.7% as Na O on the O. D.

wood) The above liquor is prepared by dilution of conventional millwhite liquor. The active alkali (A.A.) concentration of 16% A.A. basedon the O.D. wood is the same as that of a mill cook. The liquor-to-woodratio of 4.5 to 1 differs from the usual 3.4 to 1 ratio of a mill cook.

The apparatus and general procedure employed in carrying out the cooksare the same as described in Example 1. The time at the maximum cookingtemperature of 170 C. is varied from 4 to 39 minutes to provide pulps atvarious yields for comparison with those of comparable yields andwherein were utilized the treating liquors of Examples 1, 2 and 3.

This example illustrates three different simulated labo- Tables VIA andVIB follow.

TABLE VI-A Laboratory Kraft Cooks of Southern Pinewood at 16% ActiveAlkali 1 Cooking Conditions Pulp Data Pulp Carbo- Pulp hydrate (Per-Sulfidrty Effective pH Time Yield Lignin cent of Initial Cook No.ChemJlOO g. Wood (Percent) Alkali 1 Range (min.) (Percent) (Percent)O.D. Wood) 6.7 g. Nags, 13.8 g. NaOH 5.0 g. NazCOg 33.1 13.4 13 5 to13.l 39 55. 9 13. 4 48. 4 6- Same as above 33. 1 13. 4 13 5 to 13.3 1260.8 18.9 49. 3 15-0 d 33. 1 13. 4 13 5 to13.3- 4 64. 3 20. 6 51. 1

1 Calculated as NazO and based on the O.D. weight of the wood.

TABLE VI-B Tests on 26 lb./MSF Papers Made from Pulps of Cooks of TableVI-A Papers Mead Williams Dry Ring Bright- From Refine Slowness DensityTensile Tear Mullen Crush ness Cook No. Time (See) (Sec) (p.c.i.)(lbs/in.) (g./16 sh.) (p.s.i.) (lbs.) (Percent) S a 153 55. 33. 2 53. 9197 109 70. 0 18. 8 205 55. 0 30. 1 44. 3 177 90 65. 0 17. 8 217 55. 030. 2 42. 5 178 81 60. 0 18. 7

EXAMPLE 6 than that which results from comparable soda pulping Thisexample illustrates the pulping of isopropanolextracted southernpinewood by means of a one-stage treatment with alkaline liquorcomprised of varying amounts of 2-mercaptoethanol (instead of TGA in theform of its sodium salt as in the other examples utilizing andorganomercaptan) at 8 and 16 weight percent effective (and active)alkali calculated as Na O based on the OD. wood. The time at maximumtemperature (i.e., 170 C.) is varied from 39 to 120 minutes. A soda cookat 16 weight percent effective (and active) alkali concentration isprovided for comparison. The apparatus and general procedure are thesame as that described in Example 1.

In all cooks the maximum temperature of digestion is 170 C. and theliquor-to-wood ratio is 4.5 to 1. Other details on the cookingconditions are given in Table VII-A and the properties of the papersmade from the pulps are given in Table VII-B. The data on one-stagealkaline pulping with 2-mercaptoethanol that are given in these tablesprovide additional evidence of the improvements that result in thepulping of lignocellulosic material when the alkaline liquor iscomprised of an organomercaptan. The pH data of the cooks in Table VIshow the lowering and control of the liquor pH that is is shown to beachieved when 2-mercaptoethanol is included in the pulping liquor. Thehigher yield of carbohydrate (i.e., 51.1% of the initial wood) and thelower lignin content of the pulp (i.e., 20.1%) resulting from theZ-mercaptoethanol Cook No. 7-b, when compared with the results from sodaCook No. 7-a (i.e., 47.4% carbohydrate yield and 24.4% pulp lignin),provide evidence of these facts.

In addition, the data show that a one-stage process of this inventionwherein Z-mercaptoethanol is utilized as the organomercaptan (also withTGA in the form of its sodium salt) provides a pulp of good quality in ahigh yield. Considerable improvement (except for brightness) in thepaper properties of the pulp over that of the soda pulp is shown toresult even at the higher pulp yields. Pulp with paper properties(tensile, Mullen, ring crush, tear, and brightness) near to orcomparable with the values of papers made from kraft-process pulp isshown by the data as being obtained even up to 63.9% yield. It isfurther to be noted that, except for brightness, papers made from thepulp of Cook No. 7-c that was obtained in a yield of 76.4% had unusuallygood properties when the very high pulp yield is considered.

Tables VII-A and VII-B follow.

TABLE VII-A Soda and Z-Mercaptoethanol (ME) Pinewood Cooks at 8% and 16%Active and Effective Alkali 1 Pulp Data Pulp Cooking ConditionsCarbohydrate I (Percent of Efiective pH T me Yield Lignin Initial O.D.ChemJlOO g. Wood Alkali 1 Range (min.) (percent) (percent) Wood) 20.7 g.NaOH, 5.0 g. NazCOa 16. 0 13.5 to 13.3.- 39 62. 7 24. 4 47. 4 42.4 g.ME, 20.7 g. NaOH 16. 0 10.4 to 11.4.- 39 63. 9 20. 1 51. 1 21.2 g. ME,103 g. NaOH 8.0 10.2 to 9.5... 120 76. 4 27. 5 55. 4

1 See Footnote to Table I-A.

TABLE VII-B Tests on 26 lb./MSF Papers Made from Pulps of Cooks of TableVII-A Papers Mead Williams D13 Ring From Refined Slowness DensityTensile Tear Mullen Crush Brightness Cook No. Time (Sec) (See) (p.c.i.)(lbs/in.) (g./16 sh.) (p.s.i.) (lbs) (percent) 193 55. 0 27. 8 39. 5 14771 52 19. 7 153 55. 0 28. 6 47. 8 192 88 59 16. 4 124 55. 0 31. 9 46. 7150 82 74 12. 5

provided by the organomercaptan employed, viz, Z-mer- EXAMPLE 7captoethanol. The advantages resulting from this pH control (i.e., indecreasing the high loss of carbohydrate material that normally resultsfrom hydrolytic attack by alkali during alkaline pulping) and from thereaction of the Z-mercaptoethanol with the lignin of the wood are shownmost pronouncedly by comparison of Cook No. 7-b with soda Cook No. 7-awhich is carried out under the same cooking conditions and concentrationof effective (and active) alkali.

The data in these tables show that improvements similar to thosedemonstrated in previous examples with TGA in the form of its sodiumsalt also result with Z-mercaptoe h ol More o p te and mo e s l ct edelig iifica icii This example illustrates the pulping of a hardwood,specifically black gum, with an alkaline liquor comprised of TGA in theform of its sodium salt, i.e., sodium thioglycola-te (NaTGA). The liquoris comprised of varying amounts of NaTGA at 8 weight percent effective(and active) alkali concentration calculated as Na O and based on theweight of the OD. Wood. Two soda cooks, one under the same cookingconditions as the NaTGA cooks and the other differing from the NaTGAcooks only in the time (12 minutes) at the maximum cooking tem perature,are provided for comparison. The apparatus and the general procedure arethe same as that described 21 in Example 1. In all cooks the maximumtemperature of digestion is 170 C. and the liquor-to-wood ratio is 4.5to 1. Other details on the cooking conditions are given in Table VIIIAand the properties of papers made from the pulps are given in TableV-III-B.

The data in Tables VIII-A and VIIIB show the improvements that resultover comparable soda pulping when black gum is pulped with soda liquorcomprised of an organomercaptan, specifically NaTGA. Evidence ofimprovements similar to those described in the previous examplesdirected to the pulping of a softwood (specifically pinewood), is, ingeneral, provided. The only major difference between the organomercaptanpulping of the two different woods, that is, black gum and pine, appearsto be the relatively low tear strength of the paper made from the blackgum pulp. This is a normal char-acteristic for paper made from this typeof hardwood by prior-art pulping methods.

The pH data of the NaTGA Cook Nos. 8a and 8-b in Table VIII-A, whencompared with that of soda Cook Nos. 8a and 8a, show the control of theliquor pH that is provided by the organomercaptan, specifically NaTGA,and which has been described more fully in previous examples. The effectthat this control has in decreasing the loss of carbohydrates is shown(Cook Nos. 8a and 8b) by the higher yields of carbohydrate (53.555.3%based on the initial weight of the OD. wood) in the pulps resulting fromthe NaTGA cooks .as compared with the pulp carbohydrate yields (51.5%based on the weight of the initial O.D. wood) resulting from soda CookNos. 8c and 8-d.

The data also show the improved dissolution of the wood lignin (i.e.,the more complete delignification) that is obtained by pulping withNaTGA as compared with soda pulping. Much less lignin (16.4-17.1%) isleft in the pulps of Cooks Nos. 8a and 8-b as compared with the amountof lignin (25.0%) left in the pulp of soda Cook No. 8-d and wherein thecooking conditions are the same including the time at the maximumtemperature.

The paper data in Table VII'L-B show that black gum pulp made by themethod of this invention (Cook Nos. 8a and 8-b) can be expected toprovide papers having much better properties, especially as to tensile,Mullen, ring crush, and brightness values than soda pulp at comparableyields. In fact the properties, except for tear strength, areexceptionally good when one takes into consideration the high yield andthe fact that the pulp originates from a hardwood.

Tables VIII-A and VIII-B follow.

TABLE VIII-A TGA and Soda Black Gum Cooks at 8% Active and EffectiveAlkali 1 Instead of using thioglycolic acid or 2-mercaptoetha- 1101 asthe organomercaptan that is incorporated into the alkaline treatingliquor in Examples 1 through 4, 6, and 7, similar results are obtainedby using an equivalent amount of other organomercaptans including othermercaptocarboxylic acids such as mercaptopropionic acid, HSCH -CH COOH,and higher members of the homologous series ofmonomercaptomonocarboxylic acids, and acids the formulas of whichpreviously have been identified in Formulas VI through X. Or, one mayuse 3-mercaptopropanol or higher members of the homologous series ofmercaptoalkanols; or other organomercaptans of which numerous examplespreviously have been given. Also, instead of pulping a softwood (e.g.southern pinewood), or a hardwood (e.g., black gum wood) by digestionwith a treating liquor containing an organomercaptan as described inExamples 1 through 4, 6, and 7, a similar treatment may be applied to amixture of a softwood and a hardwood, e.g., a mixture f southernpinewood and black gum wood.

From the foregoing description it will be seen that the presentinvention provides a method of treating lignocellulosic material for theremoval of lignin therefrom which comprises:

(A) Digesting said material with a treating liquor containing an agentreactive with the said lignocellulosic material and which is comprisedof an organomercaptan in an amount corresponding to at least about 2weight percent and preferably at least about 5 weight percent based onthe weight of the OD lignocellulosic material. The treating liquorcontains alkali equivalent to at least about 2 weight percent effectivealkali calculated as Na O, or at least 4 weight percent total alkalialso calculated as Na O, these weight percentages being based on theWeight of the OD lignocellulosic material.

The amount of the aforesaid effective alkali or of the aforesaid totalalkali, the ratio of treating liquor to DD. lignocellulosic material,and the time and temperature of digestion are such as to cause theorganomercaptan component of the treating liquor to react with thelignin in the lignocellulosic material and concurrently to extracttherefrom the resulting mercaptan-reacted lignin so that there isobtained in a single stage digested, solid, cellulosecontaining materialwhich is amenable to refining to a pulp, more particularly apaper-making pulp. Ordinarily, this cellulose-containing material alsocontains lignin in varying amounts.

As previously has been indicated the treating liquor also may contain aninorganic thio compound, more par- Pulp Data Cooking Conditions PulpCarbo- Pulp hydrate (Per- Cook Time Yield Lignin cent of Initial N0.Chem./ g. Wood pH Range (min) (percent) (percent) O.D. Wood) 8a 31.0 g.NaTGA, (25.0 g. TGA), 10.3 g. NaOH 10.6 to 10.2 39 64. 5 17.1 53. 5 8b61.9 g. NaTGA, (50.0 g. TGA), 10.3 g. NaOH 9.2 to 8.7 39 66.1 16. 4 55.38-c 10.3 g. NaOH 13.0 to 11.7-- 12 69. 9 26.4 51. 5 8(1 10.3 g. NaOH12.9 to 11.7 39 68. 7 25.0 51. 5

1 See Footnote to Table I-A.

TABLE VIII-B Tests on 20 lb./MSF Papers Made from Pulps of Cooks ofTable VIII-A Mead Papers Refine Williams Dry Ring From Time SlownessDensity Tensile Tear Mullen Crush Brightness Cook N 0. (Sec) (See)(p.c.f.) (lb/in.) (g./16 sh.) (p.s.i.) (lbs) (percent) .cularly aninorganic sulfide such as Na s or an inorganic ydrosulfide such as NaSH,in an amount that may be aried considerably depending upon theparticular reults that are desired. Usually, if an inorganic thiocomound is added to the treating liquor in practicing the resentinvention, it is employed in a minor amount (i.e., ass than 50 weightpercent) of the total SH content f the treating liquor. Preferably sucha modifying inrgani-c thio compound is a water-soluble inorganic hy-.rosulfide, e.g., an alkali hydrosulfide such as sodium, iotassium,lithium or other alkali-metal hydrosulfide, or heir obvious equivalents;and the amount thereof is genrall from about 3 to about 45 weightpercent, more paricularly from about to about 30 weight percent, of hetotal SH content of the treating liquor.

(B) At the end of the digestion period, the excess liquor s removed byany suitable means from the digester, e.g., vy draining, siphoning,etc., thereby separating the excess iquor from the treated materialresulting from Step A.

Preferably the residue that remains after removing the :xcess liquorfrom the organomercaptan-treated lignoaellulosic material is washed,e.g., with water and, more iarticularly, with hot water. The washedresidue may then 1e refined, as desired or as may be required, to yielda mi suitable for paper-making or other purposes. Addiionally, ifdesired, it may be bleached or further processed 1S desired or asrequired for the particular end use.

From the foregoing description of the instant invention t will be seenthat it is materially and unobviously differ- :nt from that described byHolmberg in the early part of :his specification, and is separately andpatentably distinct from that disclosed and claimed in ouraforementioned copending application Ser. No. 605,978 and in our:opending application Ser. No. 606,025. It is also separately andpatentably distinct from the inventions disclosed and claimed in thecopending applications of Carl A. Iohnson, Ser. No. 606,024 and Ser. No.606,012. The first identified Johnson application is concerned with theuse of a combination of an organomercaptan and a hydrotrope agent in amethod for pulping (digesting) lignocellulosic material. The latterJohnson application is concerned with a particular two-stage treatmentto delignify (pulp) lignocellulosic material first with a treatingliquor containing an organomercaptan and having an alkaline pH up toabout 12.0; and, in a second stage, extracting mercaptanreacted ligninretained by the digested lignocellulosic material by contacting it witha dilute solution of a watersoluble inorganic base. All of theaforementioned applications, filed concurrently herewith, are assignedto the same assignee as the instant invention.

We claim:

1. The method of treating lignocellulosic material for the removal oflignin therefrom in a single stage which comprises:

(A) digesting said material with a treating liquor containing an agentreactive with the said lignocellulosic material and which is comprisedof an organomercaptan in an amount corresponding to at least about 2weight percent based on the weight of the ovendried lignocellulosicmaterial, said treating liquor containing alkali equivalent to at leastabout 2 weight percent effective alkali calculated as Na O, or at least4 weight percent total alkali also calculated as N320, said weightpercents being based on the weight of the oven-dried lignocellulosicmaterial,

the amount of the said alkali, the ratio of treating liquor tooven-dried lignocellulosic material, and the time and temperature ofdigestion being such as to cause the said organomercaptan to react withthe lignin in the said lignocellulosic material and concurrently toextract therefrom the resulting mercaptan-reacted lignin so that thereis obtained in a single stage a digested, solid, cellulose-containingmaterial that is amenable to refining to a pulp; and

(B) removing the excess liquor from the treated material from Step A.

2. The method as in claim 1 wherein the lignocellulosic material issoftwood.

3. The method as in claim 1 wherein the lignocellulosic material ishardwood.

4. The method as in claim 1 which includes the step of washing theresidue that remains after removing the excess liquor from theorganomercaptan-treated lignocellulosic material.

5. The method as in claim 1 wherein the organomercaptan is onerepresented by the general formula wherein Z represents an alkyleneradical containing from 1 through 10 carbon atoms; R represents a memberof the group consisting of (a) hydrogen, (b) alkyl radicals containingnot more than 10 carbon atoms, and (c) a saltforming cation; and nrepresents an integer from 1 up to that of the combining power of thealkylene radical represented by Z; and which includes the step ofwashing the residue that remains after removing the excess liquor fromthe organomercaptan-treated lignocellulosic material.

6. The method as in claim 5 wherein the organomercaptan introduced intothe treating liquor is one represented by the general formula wherein nrepresents an integer from 1 to 8, inclusive, and R represents a memberof the group consisting of (a) hydrogen, (b) alkyl radicals containingnot more than about 8 carbon atoms, and (c) a salt-forming cation.

7. The method as in claim 6 wherein the organomercaptan is thioglycolicacid.

8. The method as in claim 7 wherein the amount of the thioglycolic acidis less than the chemically equivalent amount of the effective alkali.

9. The method as in claim 1 wherein the weight percent oforganomercaptan is at least about 2.5.

10. The method as in claim 1 wherein the weight percent oforganomercaptan is at least about 5'.

11. The method as in claim 1 wherein the treating liquor contains from 2to about 250 weight percent of effective alkali, calculated as Na O,based on the weight of the oven-dried lignocellulosic material; theorganomercaptan is present in the treating liquor in an amountcorresponding to from 2.5 to about weight percent based on the weight ofthe oven-dried lignocellulosic material; the ratio of treating liquor tooven-dried lignocellulosic material corresponds to from about 15 toabout 200 ml. of the former for each 10 grams of the latter; and themaximum digestion temperature is within the range of from 100 C. to 250C.

12. The method as in claim 1 wherein the organomercaptan, as introducedinto the treating liquor, is thioglycolic acid in an amountcorresponding to from about 5 to about 50 weight percent based on theweight of the oven-dried lignocellulosic material; the treating liquorcontains at least 6.5 weight percent of effective alkali, calculated asNa O, based on the weight of the oven-dried lignocellulosic material;and the ratio of treating liquor to oven-dried lignocellulosic materialis from about 30 to about 60 ml. of the former for each 10 grams of thelatter.

13. The method as in claim 1 wherein the organomercaptan, as introducedinto the treating liquor, is thioglycolic acid in amount correspondingto from about 5 to about 50 weight percent based on the weight of theovendried lignocellulosic material; the maximum digestion tentperatureis within the range of from 100 C. to 250 C.; and the time of digestionat the maximum temperature is within the range of from a few minutes to6 hours.

14. The method as in claim 13 wherein the digestion temperature iswithin the range of from C. to 210 0; an he time of digestion at themaximum temperature is within the range of from about hour to about 3hours.

15. The method as in claim 13 wherein the maximum digestion temperatureis within the range of from 150 C. to 190 C.; the time of digestion atthe maximum temperature is within the range of from about hour to about3 hours; and which includes the step of water-washing the residue thatremains after removing the excess liquor from theorganomercaptan-treated lignocellulosic material.

16. The method as in claim 4 which includes the additional step ofrefining the washed residue to a papermaking pulp.

17. The method as in claim 15 wherein the organomercaptan-treatedlignocellulosic material is organomercaptan-treated pinewood; the ratioof treating liquor to ovendried lignocellulosic material corresponds toabout 45 ml. of the former for each 10 grams of the latter; thedigestion temperature is about 170 C.; and the time of digestion at themaximum temperature is from about /2 to about 1 hour.

18. The method as in claim 1 wherein the organomercaptan isZ-mercaptoethanol.

19. The method as in claim 1 wherein the organomercaptan is amercaptoalkanol.

20. The method as in claim 1 wherein the treating liquor also contains aminor amount by weight of an inorganic thio compound.

References Cited Wood Chemistry, Wise and Jahn, 2nd ed., vol. I,published by Reinhold Pub. Corp., New York, N.Y., 1952, p. 435, and p.498.

HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 16271, 77

